1) $$p^2 + 10p + 25 = (p + 5)^2$$
2) $$-100 + 0,09c^2 = 0,09c^2 - 100 = (0,3c)^2 - 10^2 = (0,3c - 10)(0,3c + 10)$$
3) $$81p^2m^2 - n^2 = (9pm)^2 - n^2 = (9pm - n)(9pm + n)$$
**Ответ:**
1) $$(p + 5)^2$$
2) $$(0,3c - 10)(0,3c + 10)$$
3) $$(9pm - n)(9pm + n)$$